Accepted_test

During their lifetime, plants are exposed to complex stress factors, which lead to significant yield losses and stimulate defense mechanisms. It is remarkable that plants are able to retain information about stressful events (inherited stress memory) and optimize their reactions to repeated stresses. The aim of our work was to determine the possible involvement of circadian rhythm genes in tomato plant response to stress factors. The adaptive evolution of plants is associated with the circadian rhythms – repetitive fluctuations in molecular genetic processes with a 24-h period. To assess the effects of a cold stress at night in tomato seedlings, the expression of the circadian rhythm (GIGANTEA, FKF, CONSTANS) and photosystems (psaA, psbA) genes was determined, and the chlorophyll content was measured. All the genes showed differential expression: cold exposure increased circadian fluctuations in the expression in various degrees. Temperature dependence was also present for the content of chlorophylls. In the case of repeated cold stress effects in the dark phase, the photosystem genes were characterized by similar changes in the expression level in each cycle of stress repeats, whereas circadian system genes changed their expression pattern in relation to the level of change. It can be assumed that the genes of circadian rhythm and photosystems are involved in the response of tomato plants to cold stress. The dynamics of expression of these genes in cold stress response may be associated with the cold resistance of tomato varieties.